[Coordinate system, see[28]:] Euclidean (orthonormal) system. The scattering plane, defined by the direction of the incident and final wave vectors
and
, contains
lying perpendicular and in the sense of
and
parallel to the scattering vector
. [Polarisation of the Photon beam:]
and
refer to the polarisation of the beam parallel and perpendicular to
, respectively. [Angles for azimuth
:]
,
, where
and
is the projection of
onto the plane perpendicular to
. In the chosen experimental geometry azimuth
, when
points to the x-ray source.